While the etiology of chest wall instability varies across age-range, the need for stabilization of the anterior chest wall is applicable to both pediatric and adult populations.
With respect to the pediatric population, marked reduction in the compliance of the lung relative to the chest wall contributes to pulmonary insufficiency, particularly in the prematurely born infant. An imbalance of forces across the chest wall caused by greater recoil of the lungs inward relative to the chest wall outward, results in reduced resting lung volume. Furthermore, because the rib cage is incompletely ossified and the respiratory muscles are underdeveloped, the chest wall of the newborn is vulnerable to inward distortion during inspiration. Respiratory efforts are dissipated on distorting the chest wall rather than effectively exchanging tidal volumes. Distortion of the chest wall during inspiration is characterized by varying degrees of anterior-posterior motion at the xyphoid-sternal junction (anterior retraction), inward motion between or within the intercostals spaces (intercostals retraction), inward motion below the lower rib cage margin (subcostal retraction), and asynchronous/paradoxical motion between the chest wall and abdomen.
Surgical and ventilatory therapies have been used to mitigate anterior retraction of the chest wall for the pediatric population, in order to increase lung volume and promote effective inspiration. In neonates with respiratory distress syndrome, “xiphoid hook”, continuous negative extrathoracic pressure (CNP) and continuous positive airway pressure (CPAP) have been shown to reduce anterior chest wall retraction and improve respiratory indices. However, all of these tools have limitations. The surgical approach is problematic because of tissue fragility. CNP ventilation is challenging because it typically requires complex ventilation units, tight seals, and has been associated with adverse effects (e.g., gastric and intestinal distention). CPAP delivered by way of nasal cannulae or prongs (NCPAP), which is the most common means of pressure support in spontaneously breathing neonate, improves lung volume and oxygenation and reduces chest wall distortion. NCPAP is not completely benign, however, mostly due to complications such as inconsistency in, and loss of, distending pressure with an open mouth or poor fitting nasal prongs, nasal trauma as well as gaseous distention of the abdomen. Positive end-expiratory pressure (PEEP) supports lung volume and the relatively flaccid chest wall during mechanical ventilation. High PEEP, however, may impair cardiac output, contribute to ventilation-perfusion mismatch and ventilator-induced lung injury.
With respect to the adult population, there are numerous clinical conditions causing anterior chest wall instability with pulmonary complications, such as neuromuscular and musculoskeletal disorders. Acute flail chest, for example, is one of the most common serious traumatic injuries to the thorax with morbidity linked to the acute underlying lung consequences. Flail chest is traditionally described as a paradoxical movement of a segment of chest wall caused by fractures of 3 or more ribs broken in 2 or more places, anteriorly and posteriorly, and unable to contribute to lung expansion. Acute intervention since the late 1950's includes “firm strapping” of the affected area to prevent the flail-like motion, laying the patient with the flail segment down to prevent it from moving out paradoxically during expiration, the use of towel clips placed around rib segments and placed in traction to stabilize the rib cage, intubation with positive pressure ventilation to stent the ribcage, and surgical approaches in which both ends of a fractured rib must be stabilized for operative intervention to be most effective. There is, however, a high level of long-term disability in patients sustaining flail chest characterized by a 22% disability rate with over 63% having long-term problems, including persistent chest wall pain, deformity, and dyspnea on exertion.